1. Field of the Invention
The present invention generally relates to independent suspension systems for vehicles and, more particularly, is concerned with an independent suspension system with improved vertical alignment and range of travel.
2. Description of the Prior Art
Various independent suspension systems for vehicles are known in the prior art. One example is the independent suspension system provided on model F-100 and F-250 trucks by Ford Motor Company as early as 1975. More recently, an agricultural boom sprayer illustrated and described in U.S. Pat. No. 5,353,988 to Gallenberg adopted a substantially similar independent suspension system as originally provided in the Ford trucks.
The independent suspension system on the Ford truck and Gallenberg boom sprayer includes a pair of generally horizontally-disposed elongated axle members for supporting a pair of vehicle wheels adjacent to opposite sides of the vehicle chassis. Each of the axle members independent of one another interconnects a corresponding one of the rotatable wheels with an opposite side of the chassis. One end of the each axle member is pivotally connected to the one rotatable wheel via a kingpin assembly while the opposite end of each axle member is pivotally connected to the one opposite side of the chassis. The axle members are generally straight, extend parallel to one another and pivot in generally parallel vertical planes.
The independent suspension system on the Ford truck and Gallenberg boom sprayer also includes a pair of stabilizing bars or struts interconnecting the axle members at their one ends with portions of the opposite sides of chassis longitudinally spaced from the side portions of the chassis where the axle members are pivotally connected at their other ends. Particularly, each strut is rigidly secured to the one end of the respective axle member relative to vertical pivotal movement thereof and pivotally connected to the longitudinally spaced side portions of the chassis.
The independent suspension system on the Ford truck and Gallenberg boom sprayer further includes spring means positioned between the chassis and the one end of each axle member for cushioning the vehicle as it traverses the terrain. The spring means on the Ford truck is a heavy coiled spring whereas the spring means used on the Gallenberg boom sprayer is an air bag.
The above-described prior art independent suspension system appears to provide adequate stability for the limited range of vertical travel of the suspension system, such as a few inches up or down from a neutral position, required in the vehicles using the design. However, this prior art suspension system is not seen to provide adequate stability for heavier vehicles where a significantly greater range of vertical travel of the suspension system is required from the neutral position. Furthermore, because the stabilizing struts are fixed to the axle member, the vertical alignment of the centers of the wheels relative to a vertical reference substantially changes as the wheels move away from (above or below) the neutral position. This change is tolerable in the case of lighter vehicles where the required range of vertical travel is slight. This change would not be tolerable in the case of heavier vehicles where the required range of vertical travel is much greater.
Consequently, a need exists for an independent suspension system which will accommodate the conditions and requirements encountered with heavier vehicles.